Air-to-air refuelling, also known as aerial refuelling and in-flight refuelling, is the process of transferring fuel from one aircraft (a tanker) to another aircraft during flight.
Typically, the use of radio frequency (RF) communications during air-to-air refuelling operations is not permitted due to the risk of fuel ignition.
For manned aircraft, communication via lights and hand signals is implemented. However, such methods of communication tend not to be useable for unmanned aircraft.
In a separate field to the field of aircraft refuelling, it is often desirable to transfer data, for example mission data, from an unmanned aircraft to a different entity (e.g. a different aircraft).